(1) Field of the Invention.
This invention relates to the treatment of bodies of water such as lakes with various treatment agents to improve the quality of the water or alleviate other undesirable aquatic conditions. More particularly, the invention relates to the accurate application of chemical, biological and other treatment agents to bodies of water by the use of floating platforms such as boats and the like. More particularly still, the invention provides an apparatus and method for applying such treatment agents to bodies of water on a uniform and effective basis designed to overcome or mitigate undesirable chemical or other conditions or balances, i.e. to correct predetermined chemical, biological and other imbalances in such bodies of water. The invention involves concurrent detection of parameters by which the volume of water and/or the area of the bottom to be treated is accurately and substantially continuously determined and application of the treatment agent is controlled.
(2) Description of the Prior Art.
In recent years, various problems with pollution and other deleterious imbalances in various aquatic environments have become of major concern. One such environmental problem has been that of lake acidification. Lake acidification results largely from so-called "acid rain" which recently has become increasingly serious. While acidification problems are not new and a variety of techniques have been employed in the past to counteract the adverse effects of excess concentrations of acid in lakes and other bodies of water, the problem in recent years has become particularly acute in the industrialized nations. This is due in large part, it is believed, to the increasing use of combustion processes, and particularly those combustion processes which use high sulfur fuel. Coal and oil, which are ultimately derived from biological residues, frequently contain fairly high levels of sulfur derived not only from the original biological material, but in addition to sulfur brought in from various sources and especially by perculating sulfur compound laden water. Such sulfur compounds are oxidized when the fuel is burned and the sulfur oxides generated pass into the atmosphere where they are dispersed, particularly down-wind. Upon subsequent precipitation from the atmosphere, particularly during rain and the like, such sulfur oxides are combined with atmospheric moisture to form sulfurous, sulfuric and other sulfur acids which give rise to multiple detrimental effects, including damage to biological systems, both in the air and in the water, general deterioration of the environment, progressive destruction of man-made structures and the like.
In addition to sulfur compounds which are given off by the burning of fossil fuels, high temperature combusion processes also form the so-called NOX gases, i.e. the various nitrogen oxides including NO, NO.sub.2 and the like, which upon being washed or precipitated from the air with moisture in the form of rain, snow and mist also form acid solutions which have detrimental environmental effects. Since precipitation in the form of rain ultimately collects in ground water and natural bodies of water such as lakes and the like, such bodies of water tend to suffer from an increasing content of both sulfur and nitrogen acids with serious detrimental effects upon the flora and fauna of the aquatic environment. While lakes and other bodies of water are normally slowly neutralized by natural processes, particularly in limestone regions, the continued receipt of acidified precipitation into such lakes and other bodies of water frequently proceeds at a faster rate than the natural neutralization of the acid within such bodies of water. Small degrees of acidification harms aquatic organisms through the inhibition of reproduction and growth, and in more extreme cases, causes almost complete mortality. In addition, the acidification of lakes, streams and other bodies of water increases the soluble aluminum content of the water which is particularly harmful to young fish. The solubility of other toxic metals such as copper, cadmium, mercury, lead and the like heavy metals is also increased by excessive acidity with detrimental results to acquatic and marine life in general. The acidification of lakes and other bodies of water, even of a fairly small degree, can also very seriously affect the ecological balance in such bodies of water with serious environmental and economic effects.
The acidification of lakes, streams and other bodies of water, is as noted above, not a new phenomenon. However, it is an increasingly serious phenomenon. In the past, a variety of techniques have been employed to counteract or mitigate the adverse effects of excess concentrations of acid in bodies of water. For example, American farmers may use millions of tons of neutralizing agents every year to counteract the acidity produced by nitrates and sulfates in chemical fertilizers. Furthermore, since the middle of this century, governmental agencies and private groups in the United States have used a variety of neutralization techniques to protect fish production in acid lakes and other aquatic environments. The problem with acid lakes has been particularly severe in the Eastern United States and the Scandanavian Peninsula in Europe. The reason for the particular problem in both these areas is the fact that they receive prevailing winds from other industrialized areas and a considerable amount of precipitation, all of which tends to remove acid components which have entered the atmosphere in other regions from both industrial and transportation combustion processes used in such regions. Since, as indicated above, acidified waters tend to collect in lakes, unless there is a continuous neutralization of such waters, the lakes tend to become increasingly acidified, often to the point where not only native plants and fish are killed, but essentially all but very specialized organisms are very adversely affected, if not completely destroyed.
While a large proportion of the acid lake problem is due to so-called acid rain, as explained above, other industrial and agricultural practices also add to the acid lake problem. For example, nitrogen and sulfur containing fertilizers may leach into the ground water or run off into natural bodies of water resulting in detrimental acidification of such bodies and poisoning of desirable organisms. Sulfur acids may also form in coal seams which have been opened and exposed to the atmosphere as well as to water from various sources and may also be formed from the iron pyrites or iron sulfur compounds in waste coal or culm piles and then leached into surface and ground waters.
While acid rain and the resulting lake acidification presently constitute one of the most widely recognized or notorious chemical imbalance problems in lakes and other bodies of water, other chemical and biological imbalances are equally, if not more, important. Chief among these, and perhaps the second most widely known, is so called eutrophication, or algal bloom, caused by excess nutrients in a lake. Such excess nutrients include the various chemical elements and compounds such as carbon dioxide, oxygen, nitrogen, phosphorus and minerals required for biological growth. An excess of such growth nutrients very frequently results in dramatic and, in effect, out of control overgrowth of certain acquatic organisms such as algae. Such overgrowth frequently chokes out essentially all other organisms and can become so severe that the overgrown or overblooming organism poisons itself with its own metabolic products. This can result in great quantities of decaying organic refuse which essentially poisons the waters for other organisms other than putrifactive type organisms.
Excessive discharge of organic materials such as sewage and the like into a lake or other body of water can provide so much of the essential nutrients which algae, plants and other aquatic organisms require that very excessive algal growth can occur with disasterous esthetic and ecological results. A clear pristine lake can in such manner be within a very short period converted into a choked swamp. Severe algal overgrowth may also result in serious depletion or even complete removal of essential nutrient elements from the water with resultant mortality of a balanced aquatic population and eventual death and putrification even of the overgrown algae due to lack of essential nutrients.
Water run off from inorganically fertilized farm lands can not only cause detrimentally acid aquatic conditions, but can also cause eutrophication due to excessive nutrients entering the water. Organic fertilizer run-off may also result in eutrophication in nearby waterways.
Control of eutrophication is usually accomplished by controlling one of the more essential nutrients, usually phosphorus, which is relatively scarce, but very essential, and thus more easily controlled than some of the other more common essential nutrients. Even when the phosphorus content of the water is controlled, however, residual phosphorus can be released from sediments already in the lake, prolonging the enriched state and supporting continued algal bloom or eutrophication.
Lakes and other bodies of water may also acquire other types of chemical imbalances, one frequent one being over basicity or alkalinity caused by excessive content of basic substances such as in particular, calcium carbonate derived from limestone and lime fertilizers. In hard water region lakes, a so-called "whiting" phenomenon sometimes occurs in the warmer productive periods of the year. Such "whiting" is caused by calcium carbonate precipitation which causes major increases in turbidity of the water, deleteriously affecting water quality. In such cases, it may be necessary to add acid or acidic materials to the water to counteract the basicity. Such acid materials obviously must be carefully added to prevent over-acidification resulting in the same problems as that caused by acid rain and the like.
Other additions which may be made to lakes and other bodies of water at various times may be algacides, such as copper sulfate, to kill excessive algae, fertilizers to encourage the growth of photosynthetic and other fish food, general or specific herbicides to kill excessive or deleterious multicellular plant growth, disinfectants or poisons to sterilize a body of water and other treatment agents for various specialized purposes.
One method of counteracting the acid rain and acid lake problems is by neutralization of the affected lakes and other bodies of water by various neutralizing agents. Rehabilitation of surface waters has been experimentally practiced with a number of reagents, including lye, sodium carbonate, calcitic and dolomitic limestones, hydrated lime, quicklime and slurried industrial slags, which are essentially calcitic or dolomitic lime material. Calcitic limestone has proved for a number of reasons to be the material of choice, particularly since it is readily available and relatively cheap. Calcitic limestone is comprised primarily of calcium carbonate and is a natural solution component of many lakes and streams where it acts as a buffering agent. Calcitic limestone also has a moderate reactivity which protects fish against so called pH shock. It may also be relatively easily prepared in slurries or solutions applicable to a variety of acidic conditions.
Slurries and solutions of calcitic limestone, usually in the form of a slurry, have been applied to lakes and other bodies of water by means of boats and by helicopters, usually by spraying the slurry from a hose into the body of water. Normally the pH of the body of water is first established and the volume of water in such body is at least roughly estimated or determined, after which the amount of calcium slurry necessary for application to the body of water in order to neutralize the acid content of the water is calculated. Refinements of the basic neutralizing agent application process have included division of a body of water arbitrarily into a number of zones and measurement of the depth of the water in each of such zones whereupon an amount of neutralization agent may be applied to each zone calculated to effect the desired raising of the pH of the water in such zone. The pH reading, of course, is a measure of the hydrogen ion content of the water. A further refinement has been the use of coarser particles of calcitic material in a limestone slurry to penetrate deeper portions of a lake or other body of water. The larger particles resist complete dissolution in the water before they reach the bottom.
It can be readily seen from the description above that the liming or neutralization of an acid lake is no small undertaking. The neutralization agent cannot be applied heedlessly to such body of water because of the cost and since the production of too basic an environment in the water may frequently be almost as harmful to aquatic life as too acid an environment. In fact, eutrophication of lakes by excessive contents of phosphates and other growth-accellerating ingredients may be accentuated by overliming of such bodies of water. Furthermore, while limestone particles which settle to the bottom of the average lake tend to sink into the bottom mud or ooze and are thus effectively removed from further affecting the basicity of the overlying water, excessive bottom limestone is thought to adversely affect adjacent aquatic plant life.
It is also undesirable to have zones of different acidity or pH in a lake, since aquatic life traveling from one zone to another may be deleteriously affected. Fish especially, and game fish, in particular, tend to be adversely affected by so-called pH shock engendered by quick changes in the pH of their environment. Zoning and stratification of pH zones in lakes is often accentuated by the slow mixing of the waters of such lakes. Consequently, it has been found very difficult to effect a uniform and accurate liming of bodies of water by the equipment and techniques heretofore used or available. This has been so, in spite of the fact that very great care is taken in the liming of lakes to try to obtain a uniform application of the liming or neutralization material, i.e. the aim is to apply a uniform amount of material to a uniform volume of water. In most cases, this has been done by first drawing up a topographical map of the lake to be treated using soundings or measurements of the depth of the lake taken in many places throughout such lake. A grid is then placed over this map and the lake is divided into zones based on the average depth of such zones. From this topographical map, the volume of the water in such zones is calculated. Next, the amount of material required for each zone for neutralization of the water in such zone is determined from the volume of water, the acidity measurements of the lake, and the neutralization value of the chemical which is to be applied to the lake. The neutralization material is then applied to the lake waters, usually from a boat or a helicopter in conformance with, or as much in conformance with as is possible, these predetermined calculations.
In actual practice, the treatment zones are usually marked in the lake by placing buoys at stratigic boundries thereabout, whereupon each zone can be treated with the precalculated amount of neutralization material. A slurry of neutralization agent in which the particles are of approximately the size which will dissolve completely as they settle from the surface to the bottom of the lake is then prepared. If the water, however, turns out to be deeper than expected, the particles may dissolve before they reach the bottom, leaving a bottom volume which has not been neutralized. Since bottom water in a lake very often is either not changed or infrequently changed by mixing, this unneutralized portion may persist for many weeks or even months. On the other hand, if the size of the particles of the slurry are too large for the depth of the water, such particles may not dissolve by the time they reach the bottom of the lake, but will settle onto the bottom and either be lost in the bottom debris or mud or form an over-neutralized zone along the bottom. This over-neutralized zone will also tend to persist over long periods due to non-mixing of the bottom waters.
In the control of eutrophication of lakes and the like, as stated earlier, the choice method of control is by limiting the availability of phosphorus in the water. Assuming it is not possible to limit the overall nutrient load entering the water from outside sources, without which there would not usually be a problem in any event, it is usually impractical, if not impossible, to limit the entrance of phosphorus into the lake or other body of water. It is thus necessary in order to control the phosphorus in the water to remove such phosphorus by precipitation, flushing or the like. The method of choice is frequently precipitation by the use of aluminum bearing materials because the formation of the resulting insoluble precipitate is not generally reversible with changed oxidation conditions and the complexes and polymers formed are also effective in removing particulate and inorganic phosphorus. Additions of aluminum compounds has been practiced in the United States and Sweden since at least 1970. The aluminum bearing materials, such as the frequently used alum, or hydrated aluminum sulfate, react chemically with the phosphorus in the water to form insoluble aluminum phosphates which precipitate, thus becoming unavailable for use. The pH of the water when the alum is added largely determines the composition of the material which precipitates. For example, when aluminum sulfate plus sodium aluminate is added to a lake, the solution pH dictates the formation of an aluminum hydroxide floc (a fine fluffy mass of particles or the like) which will settle to the bottom. As the aluminum hydroxide floc settles, phosphorus in the water column through which the floc passes is removed as aluminum phosphate precipitate, by absorption of phosphorus on the surface of the aluminum hydroxide polymer or floc and by entrapment and sedimentation of phosphorus containing particulate matter in the floc. The phosphorus is then trapped with the floc in the sediments at the bottom of the lake.
A number of other chemical reagents can be used to precipitate phosphorus such as sodium aluminate, aluminum hydroxide, clays and other aluminum bearing materials as well as lime products which can also form insoluble phosphates and some iron compounds. However, as indicated the use of alum plus preferably sodium aluminate is the method of choice.
A number of other treatment materials may also be added to lakes and other bodies of water for various reasons. For example, it may be desirable to add fertilizers, herbicides and other materials to aquatic environments to redress various possible imbalances in the aquatic environment.